Hydroentangled nonwoven fabrics with improved properties

ABSTRACT

Hydroentangled fibrous webs containing wood pulp and synthetic fibers having improved properties are prepared by impacting a fibrous web with water jets on a flattened woven plastic or metal support, or a combination of flattened and round woven supports to entangle the wood pulp and fibers.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to nonwoven fabrics containing wood pulp andsynthetic fibers made by hydroentangling a fibrous web on a flattenedwoven support member.

2. Description of the Related Art

The hydroentangling (or hydraulic needling) process for producingspunlaced nonwoven materials have been used for many years. In thehydroentangling process, a loose aggregation of fibers is positioned ona screen or some type of apertured support and subjected to a series ofhigh-pressure water jets to bind or entangle the fibers to form afabric. Also, relatively low pressure water jets (consolidator orcondensing jets) can be used in advance of the first series of mainhydroentangling jets to provide some initial structural integrity to theloose fibers. Screens or apertured support members are also used in thisconsolidation process.

Conventional hydraulic needling processes are described in U.S. Pat. No.3,485,706, to Evans, hereby incorporated by reference. The supportmember can be porous, such as a perforated plate, or a metal or plasticbelt or screen that is woven from round or other shaped strands,monofilaments, or yarns. Woven screens are generally formed from metalwires and plastic filaments that have smooth surfaces.

Alternately, as described in Smith et al. International PublicationNumber WO 2003/031711, the web-supporting member can have a surface thatincludes rough-surfaced yarns that inhibit movement of the nonwovenfiber web relative to the web-supporting surface.

U.S. Pat. No. 4,868,958 to Suzuki et al describes hydroentangling afibrous web on a smooth-surfaced plate that includes a plurality ofdrainage holes. U.S. Pat. No. 4,805,275 to Suzuki et al describes waterjet treatment of a fibrous web that includes conducting a preliminaryentangling treatment on a smooth-surfaced water-impermeable beltfollowed by entangling treatment on a plurality of smooth-surfaced waterimpermeable rolls. The water impermeable rolls are multistagedly andparallely arranged in order to provide effective draining treatment.

International Publication WO 2004/061183 describes a support belt madefrom flattened filaments used in hydroentangling processes.International Publication WO 2004/061183 describes a support belt thatis subjected to a calendering process to deform flatten at least aportion of the constituent filaments. Both are assigned to AlbanyInternational Corporation (Albany, N.Y.).

The abrasion resistance and tensile properties of hydraulicallyentangled nonwoven fabrics can be improved by increasing hydroentanglingpressures or using more powerful jets. However, these approaches canresult in a reduction in barrier properties, which is undesirable forcertain applications, such as medical fabrics. When woven belts are usedas the support member during hydroentanglement, the fibers can becomeentangled or “needled” into the woven support over time. This mayrequire physical removal of the unwanted fibers or, alternately, runningscrap scrim through the machine in an attempt to remove the errantfibers, both of which involve delay or stopping the production line.When the fibers cannot be removed from the woven support member, thesupport member usually must be replaced, typically at high cost.

There remains a need for hydraulically entangled nonwoven fabrics havingimproved physical properties such as improved abrasion resistance andstrength. In addition, there is a need for nonwoven medical fabricshaving improved barrier properties.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically depicts intersecting strands in a conventionalsupport member.

FIG. 2 depicts a ground fiber from a flattened support member.

FIG. 3 is a photomicrograph of the top surface of a fabric made using aconventional support member.

FIG. 4 is a photomicrograph of the top surface of a fabric made using aflattened support member.

FIG. 5 is a photomicrograph of the bottom surface of a fabric made usinga conventional support member.

FIG. 6 is a photomicrograph of the bottom surface of a fabric made usinga flattened support member.

DETAILED DESCRIPTION OF THE INVENTION

Woven support substrates, such as screens, used in the hydroentanglingprocess have “knuckles”, which are raised areas that are formed wherethe strands extending in one direction weave over those extending inanother direction, as depicted in FIG. 1. Strand 2 is depicted asoverlying strand 1 forming knuckle 3, representative of a conventionalwarp and weft woven pattern. The terms “flattened belt” and “flattenedscreen” as used herein refer to a woven support substrate, such as abelt or screen that has been woven from filaments or strands, whereinthe knuckle areas have been flattened after weaving. It has been foundthat significant advantages are achieved when nonwoven fabricscontaining about 5-50 % wood pulp and about 95-50% synthetic fibers aremade by using flattened belts as described herein in a hydroentanglingprocess. The advantages include improvement in properties, such as, butnot limited to tensile strength, abrasion resistance and hydrostatichead (hydrohead). Further, it has been found that “needling” issignificantly reduced with the use of flattened belts.

Also, a wood pulp/poly(ethylene terephthalate) (WP/PET) hydroentangledfabric made with flattened belts have thinner rows of wood pulp on thetop surface than fabrics that were hydroentangled on round belts.Likewise, the bottom surface of such fabrics had significantly more woodpulp distributed substantially evenly across the bottom surface comparedto the relatively thin lines of wood pulp aligned primarily in themachine direction for fabrics made on round belts. This is demonstratedin FIGS. 3-6, wherein the top surface is substantially the wood pulpside and the bottom surface is substantially the PET or polyester side.It is noted that the fabrics represented in the photomicrographs inFIGS. 3-6 were made using plastic belts in both the round form and inthe flat form. The use of a flattened belt for hydroentangling resultsin a fabric having improved barrier properties compared to fabricsobtained using a round belt, making the fabrics of the present inventionespecially suitable for use as medical fabrics and other end uses whereliquid barrier properties are desirable. The observation of improvedhydrostatic head using flattened belts was unexpected in view of thethinner rows of wood pulp observed on the WP side as observed inphotomicrographs of similar samples. Conventional wisdom is that inorder to achieve good barrier properties in wood pulp-based medicalfabrics, an even layer of unbroken WP (except for jet tracks) is desiredto act as a substrate for the fluorochemical repellent. Surprisingly,despite the thinner rows of WP on the WP side of the hydroentangledfabrics of the invention, the fabrics of the invention exhibitedimproved hydrostatic head compared to fabrics made using round belts.Without wishing to be bound by theory, it is possible that the secondarylayer of wood pulp formed on the fabric backside offers an additionalreceptor layer for the fluorochemical. It is also possible that the useof flattened belts/screens reduces the amount of wood pulp that iswashed out of the web during the hydroentangling step compared to roundbelts/screens.

When the strands are metal, the knuckle areas are flattened by removingpart of the top surface of the strands at the knuckle areas, such as bygrinding. When the top surfaces of the metal strands are partiallyground away, flattened surfaces (lands) are formed. The amount of themetal strands ground away from the knuckles on the top surface of wovenmetal screens/belts was calculated from measurements made using opticalphotomicrographs taken of the flattened surface of the belt at amagnification of 50×. The knuckle areas that were ground away appearedas ovals on the flattened surface of the screen with the major dimensionof the oval aligned with the length of the metal strands.

When the strands are plastic, the knuckles and surrounding areas areflattened by applying pressure, (with or without heat) to the knuckleareas causing the strands to deform and flatten into an ellipticalcross-sectional shape in the knuckle areas, in which case the flattenedknuckle areas are also referred to as lands. For example, a wovenplastic substrate can be calendered to form a flattened substrate asdescribed in WO 2004/061183. To determine the extent of flattening ofthe plastic strands on the top surface of flattened plasticscreens/belts, SEM photomicrographs were taken at a magnification of200× for cross-sections through the center portion of a knuckle area ofthe screen/belt. The aspect ratio of a plastic filament at the flattenedknuckle areas was calculated as provided in the Test Methods sectionbelow.

A precursor (prior to flattening) belt/screen that is woven from roundstrands is referred to herein as a “round belt” or “round screen”. Theterms “flattened belt” and “flattened screen” are not intended toinclude substrates that have been woven from flat (e.g. rectangular orsquare) strands that are not further flattened after weaving. It isunderstood that the belt or screen can be in the form of a planarsubstrate such as a belt, or can form the surface of a drum, or can beof some other arrangement known in the art.

The term “synthetic fiber” refers to various synthetic materials thatcan be used with wood pulp in nonwoven fabrics, such as polyolefin,polyamide and polyester. “Polyester” is more typically used and isintended to embrace polymers wherein at least 85% of the recurring unitsare condensation products of dicarboxylic acids and dihydroxy alcoholswith linkages created by formation of ester units. Examples ofpolyesters include poly(ethylene terephthalate) (PET),poly(1,3-propylene terephthalate), poly(1,4-butylene terephthalate), andblends and copolymers thereof.

The term “copolymer” as used herein includes random, block, alternating,and graft copolymers prepared by polymerizing two or more comonomers andthus includes dipolymers, terpolymers, etc.

The term “wood pulp” includes cellulosic material in the form of paperwebs as well as in particulate form, such as fluff and the like.

The term “machine direction” (MD) is used herein to refer to thedirection in which a nonwoven web is produced (e.g. the direction oftravel of the supporting surface upon which the fibers are laid downduring formation of the nonwoven web). The term “cross direction” (CD)refers to the direction generally perpendicular to the machine directionin the plane of the web.

TEST METHODS

In the description above and in the examples that follow, the followingtest methods were employed to determine various reported characteristicsand properties, unless noted otherwise. INDA refers to the Associationof the Nonwovens Fabric Industry. ASTM refers to the American Society ofTesting Materials.

Basis Weight (BW) of a sample was measured according to INDA StandardTest IST 130.1 (01).

Hydrostatic head (HH) is a measure of the resistance of a sheet topenetration by liquid water under a static pressure and was measuredaccording to INDA IST 80.6 (01). In the examples below, hydrostatic headwas measured for repellent-finished fabrics by placing the reservoir ofwater on the WP side of the fabric and observing the PET side of thefabric, and is reported in units of mbar. Measurements were made on thenumber of samples specified in the Examples and averaged to obtain themean hydrostatic head.

Strength of nonwoven fabrics was measured as sheet grab tensilestrength, measured according to INDA IST 110.1 (ASTM D5034-95).Measurements were made on 4-6 samples and an average strength wascalculated for both the MD and CD. The average MD and CD strengths wereaveraged to obtain the average strength for a fabric.

Martindale Abrasion is a measure of the abrasion resistance of nonwovenfabrics and was measured on the polyester side of the fabrics accordingto INDA IST 20.5 (ASTM D4966-98). Martindale Abrasion was measured on 6samples for each example and the individual results for each Examplewere averaged. Martindale Abrasion is measured on a scale of 1-6, withlower Martindale numbers corresponding to better abrasion resistance(best=1). Conditions used were150 cycles on dry fabric.

The aspect ratio of a plastic filament was calculated as the ratio ofthe minimum and maximum cross-sectional dimensions, measured at theknuckle area through the center point of a strand. Measurements weremade on two strands located on the top surface of each plastic screenand the two measurements were averaged to obtain the aspect ratiosreported in the examples below.

The percent diameter of metal strands ground away was calculated usingthe formulas found in Lang's Handbook of Chemistry, Fourth Edition(1941), Appendix, page 12. The value 100 h/D is reported in the examplesas the percent diameter ground away where h=rise and D=diameter of thestrand prior to grinding away part of the surface.) The rise is thevertical distance “h” shown in FIG. 2, measured at the center of andperpendicular to land “I” and extending to the original outer surface ofthe strand that has been ground away. Measurements of the minordimension at the center of each land (corresponding to the length ofland “I” in FIG. 2 were made on three lands per sample and 100 h/Dcalculated for each and averaged to determine the % ground away for beltCF used in Example 27 below.

Air Permeability of woven screens/belts was measured according to INDAIST 70.1 (01) (ASTM D737-96) and is reported in units of ft³/min/ft².

EXAMPLES

In the following examples, hydroentangled fabrics were prepared on alaboratory-scale table washer, on which consolidation and entanglingsteps are performed as batch processes. The table washer included acontinuous belt with speed control that runs underneath one or moreentangling jets. A secondary belt (either a flattened belt or a controlbelt (precursor to flattened belt)) was placed on the top surface of thecontinuous table washer belt and the polymeric fiber (e.g. PET) and woodpulp (WP) layers were placed on top of the secondary belt. In eachexample, a consolidation step was performed wherein the polyester webwas impacted with relatively low pressure water jets prior to adding thepaper layer, followed by running the layered WP/PET web underneath theprimary high pressure water jet for multiple passes using the specifiedjet profile to generate the desired degree of entanglement. The layeredWP/PET webs were entangled on the paper side. Some examples werehydroentangled on the same belt that was used for consolidation, whileother examples used a hydroentanglement belt that was different from theconsolidation belt.

The following codes are used to identify the screens used as supportmembers in the Examples that follow:

Belt A—Triotex 114TLM, woven plastic belt purchased from AlbanyInternational Corporation (Albany, N.Y.), aspect ratio of plasticstrands=1.0, air permeability=426 ft³/min/ft².

Belt A1F—Formed by flattening Belt A, obtained from Albany InternationalCorporation (Albany, N.Y.), aspect ratio=0.75, air permeability=318ft³/min/ft².

Belt A2F—Formed by flattening Belt A, obtained from Albany InternationalCorporation (Albany, N.Y.), aspect ratio=0.61, air permeability=285ft³/min/ft².

Belt B—Formtec 55LD, woven plastic belt with aspect ratio of plasticstrands=1.0, purchased from Albany International Corporation (Albany,N.Y.), air permeability=1140 ft³/min/ft².

Belt BF—Formed by flattening Belt B, obtained from Albany InternationalCorporation (Albany, N.Y.), aspect ratio=0.67, air permeability=705ft³/min/ft².

Belt C—75 mesh metal screen woven from round metal strands obtained fromAlbany International Corporation (Albany, N.Y.).

Belt CF—Formed by grinding the high knuckle areas of Belt C to form aflattened metal screen. The percent diameter ground away was calculatedto be about 20%.

Example 1 and Control Example A

In this example, hydraulically entangled fabrics were made using a linespeed of 75 yd/min on a table washer using flattened plastic belt A1Ffor Example 1 and precursor round plastic belt A for Control Example A.The nonwoven fabric was formed from layered wood pulp (“WP”) andpoly(ethylene terephthalate) fiber (“PET”) webs. The wood pulp (WP)paper layer was Barrier Green (H. C. Kraft) paper obtained from Domtar,Inc. (Montreal, Quebec). The PET web was a 100% PET Rando web, productcode T612 SDW obtained from DAK Americas (Charlotte, N.C.), having abasis weight of about 1 oz/yd² and denier per filament of about 1.35.The PET fiber web was pre-consolidated on belt Al F for Example 1 and onbelt A for Control Example A using a first 254 psi consolidation jetfollowed by a second 368 psi consolidation jet. Following consolidation,the WP layer was placed on top of the pre-consolidated PET web and thecombined layers hydroentangled on the same belt. The jet strip had 40holes/inch, each hole having a diameter of 5 mils. The combined WP/PETlayers were then hydroentangled with the WP layer facing the jets in 9passes, adjusting the jet pressure to simulate a series of differentjets as would be experienced in a commercial scale line. The jet profilewas 114, 170, 283,453, 906, 941, 941, 1019, and 1019 psi. Thehydroentangled fabrics were air-dried and had an average basis weight ofabout 2.0 oz/yd².

Martindale abrasion and strength properties for the hydroentangledsamples are reported in Table 1. An increase in average strength of14.7% was observed for the sample prepared on the flattened beltcompared to the sample prepared on the precursor belt. In addition, theabrasion resistance was about two times higher when the flattened beltwas used compared to the sample prepared on the precursor belt. TABLE 1Strength and Abrasion Properties for Example 1 and Comparative Example AComparative Example A Example 1 Strength, MD (lb_(f)) 27.51 30.84Strength, CD (lb_(f)) 25.62 30.09 MD Strength/CD Strength  1.07  1.02Avg Strength [(MD + CD)/2] (lb_(f)) 26.57 30.47 % Increase in AvgStrength 14.7% Martindale Abrasion 4.5 2.2

Examples 2 - 6 and Comparative Example B

These examples demonstrate combinations of round and flattened beltsused in the pre-consolidation and hydraulic entanglement steps to formWP/PET hydroentangled fabrics and the improvement achieved usingflattened belts. The PET fiber layer and WP layer used in these exampleswere the same as those described above for Example 1. The line speed was75 yd/min. The PET fiber web was pre-consolidated on either round Belt B(Examples 3-4, and Comparative Example B) or flattened Belt BF (Examples2, 5-6) using the consolidation jet pressures specified above forExample 1. After consolidation, the web was removed from theconsolidation belt and placed on the entanglement belt. After layeringwith the WP layer, the combined layers were hydroentangled on round BeltA (Example 2 and Comparative Example B), flattened Belt Al F (Examples 3and 5), or flattened Belt A2F (Examples 4 and 6) using the jet profiledescribed above for Example 1. Martindale abrasion and strengthproperties for the hydroentangled samples are reported in Table 2. Thelargest increase in average strength (about 10-12%) was observed forExamples 5 and 6, which were both consolidated and hydroentangled onflattened belts. The examples which used a combination of a round beltand a flattened belt (Examples 2-4) showed some improvement in strengthcompared to all round belts (Comparative Example B), but less than theimprovement achieved using all flattened belts. All of the Examples 2-6exhibited better abrasion resistance than Comparative Example B. TABLE 2Strength and Abrasion Properties for Examples 2-6 and ComparativeExample B Comparative Example B Example 2 Example 3 Example 4 Example 5Example 6 Belts Belt B Belt BF Belt B Belt B Belt BF Belt BF(Consolidation, Belt A Belt A Belt A1F Belt A2F Belt A1F Belt A2FHydroentanglement) Strength, MD (lb_(f)) 29.31 31.73 31.27 32.01 32.1832.07 Strength, CD (lb_(f)) 26.86 29.45 27.14 27.04 29.86 31.02 Avg. BW,MD, CD¹ 2.10,2.02 2.06,2.02 2.05,2.04 2.05,1.98 2.00,1.98 2.02,2.06(oz/yd²) MD Strength/CD  1.09  1.08  1.15  1.18  1.08  1.03 Strength AvgStrength 28.09 30.59 29.21 29.53 31.02 31.55 [(MD + CD)/2] % Increase inAvg 8.9% 4.0% 5.1% 10.4% 12.3% Strength Martindale Abrasion  1.8  1.3 1.0  1.3  1.0  1.0¹average basis weight was calculated and reported for samples used tomeasure MD strength and samples used to measure CD strength

Examples 7-11 and Comparative Example C

These examples demonstrate use of combinations of round and flattenedbelts in the consolidation and hydraulic entanglement of WP/PET nonwovenfabrics using a carded PET web instead of a Rando web, and theimprovement in strength achieved using flattened belts. In theseexamples, the WP paper was the same paper that was used in Example 1.The PET web was obtained from Hamby Textile Research (Garner, N.C.) andwas a carded web of 1.5 dpf T54 SD W PET fiber from DAK Americas(Charlotte, N.C.). The PET web was consolidated on the consolidationbelt specified below in Table 3 with a 46.3 psi jet angled at an angle θfrom the perpendicular of 30 degrees, as described in Oathout et al.U.S. patent application Publication No. US2002/0116801, which is herebyincorporated by reference, followed by three additional consolidationpasses (θ=0 degrees) at 93, 510, and 256 psi. After layering the WPlayer on the consolidated PET layer, the combined layers werehydroentangled on the same belt in three additional passes with jets at256, 194, and 324 psi, respectively, followed by transferring thecombined webs to the hydroentanglement belt. Round Belt A was used asthe hydroentanglement belt in Example 7 and Comparative Example C; BeltA1F was used in Examples 8 and 10; and Belt A2F was used in Examples 9and 11. The following jet profile was used for hydroentangling on thehydroentanglement belt: 1144, 1181, 1279, 1149, 1149, 926, and 509 psi.The line speed during consolidation and hydroentanglement was 50 yd/min.The results are shown in Table 3. All samples of the invention exhibitedhigher strength than the control example (strength increased betweenabout 13% -37%). TABLE 3 Strength Properties for Examples 7-11 andComparative Example C Comparative Example C Example 7 Example 8 Example9 Example 10 Example 11 Belts Belt B Belt BF Belt B Belt B Belt BF BeltBF Belt A Belt A Belt A1F Belt A2F Belt A1F Belt A2F Strength, MD(lb_(f)) 17.99 19.31 20.88 21.88 21.93 24.55 Strength, CD (lb_(f)) 8.8310.94 11.91 12.14 11.45 12.12 Avg. BW, MD, CD¹ 1.62,1.58 1.58,1.561.56,1.60 1.56,1.58 1.62,1.56 1.54,1.62 (oz/yd²) MD Strength/CD 2.041.77 1.75 1.80 1.92 2.03 Strength Avg Strength 13.41 15.13 16.40 17.0116.69 18.34 [(MD + CD)/2] % CD Change vs. 23.9% 34.9% 37.5% 29.7% 37.2%control % MD change vs. 7.3% 16.1% 21.6% 21.9% 36.5% control % Increasein Avg 12.8% 22.3% 26.8% 24.4% 36.8% Strength¹average basis weight was calculated and reported for samples used tomeasure MD strength and samples used to measure CD strength

Examples 12-13 and Comparative Example D

These examples demonstrate combinations of round and flattened belts,using the same WP layer that was used in Examples 7-11, and a doublelayer of the carded PET web described in Examples 7-11. Two layers ofthe PET web (instead of one layer as used in Examples 7-11) weresuperimposed and consolidated and pre-entangled as described in Examples7-11 prior to combining with the WP paper layer. Belt B was used as theconsolidation belt for Comparative Example D and Belt BF was used forExamples 12-13. The combined WP and PET layers were then hydroentangledusing the same jet profile described in Examples 7-11. Thehydroentanglement belt used in these examples was Belt A for ComparativeExample D, Belt A1F for Example 12, and Belt A2F for Example 13. All ofthe examples of the invention exhibited increased strength and improvedabrasion resistance compared to Comparative Example D. TABLE 4 Strengthand Abrasion Properties for Examples 12-13 and Comparative Example DComparative Example D Example 12 Example 13 Belts Belt B Belt BF Belt BFBelt A Belt A1F Belt A2F Strength, MD (lb_(f)) 29.56 32.95 31.75Strength, CD (lb_(f)) 15.33 18.87 16.68 Avg. BW, MD, CD¹ 2.13,2.152.10,2.12 2.10,2.12 (oz/yd²) MD Strength/CD  1.93  1.75  1.90 StrengthAvg Strength 22.45 25.91 24.22 [(MD + CD)/2] % Increase in Avg 15.4% 7.9% Strength Martindale Abrasion 1.3 1.0 1.0¹average basis weight was calculated and reported for samples used tomeasure MD strength and samples used to measure CD strength

Examples 14-16 and Comparative Example E

These examples demonstrate the effect of combinations of round andflattened belts on barrier properties of repellent-finishedhydroentangled WP/PET fabrics. The WP and PET layers used were thosedescribed above in Examples 2-6. The line speed and jet profile was alsothe same as used in Examples 2-6. A repellent finish was applied to thehydroentangled fabrics using a padder and squeeze roll setup. The padderwas a Type KLFH/K padder manufactured by Ernst Benz Ag (Sweden) andoperated at 7 yd/min and a nip pressure setting of “7” as determined bythe equipment set point. The repellent finish used was 2.5% Freepel®1225, manufactured by Freedom Chemical (Charlotte, N.C.) and 1.5% Zonyl8315 manufactured by E.I. du Pont de Nemours and Company (Wilmington,Del.), dissolved in de-ionized water. After applying the finish, thesamples were dried for two minutes at a temperature of 165° C. in aMathis Lab dryer, suspended in air with pins. Hydrostatic headmeasurements were made on four samples for each example and averaged toobtain a mean hydrostatic head. The results are shown in Table 5. Theresults show that the second belt, on which the majority ofhydroentangling occurs, has the greatest impact on the hydrostatic head.TABLE 5 Hydrostatic Head measurements for Examples 14-16 and ComparativeExample E Comparative Example E Example 14 Example 15 Example 16 BeltsBelt B Belt BF Belt B Belt BF Belt A Belt A Belt A1F Belt A1F Mean HH23.9 22.1 27.3 26.6 (mbar)1 mbar = 1.02 cm of water at 4° C.

Examples 17-21 and Comparative Examples F-J

These examples demonstrate the impact of the degree of entanglement onhydrostatic head for fabrics prepared on combinations of round andflattened belts. The degree of entanglement was varied by varying theline speed of the table washer (slower speeds=higher degree ofentanglement). The WP used was the same as that described above inExamples 2-6. The PET layer was a carded web of 1.5 denier PET fibers,Type 237 SDW from DAK Americas (Charlotte, N.C.). The PET web wasconsolidated on the consolidation belt, removed from the consolidationbelt and combined with the WP layer on the hydroentanglement belt,followed by hydroentangling. The consolidation jet pressures andhydroentangling jet profile were the same as those described inExample 1. The hydroentangled fabrics were treated with a repellentfinish as described above for examples 14-16. For each example,hydrostatic head measurements were made on six samples, each samplemeasuring 6 inches ×6 inches, and averaged to obtain a mean hydrostatichead. Sample weights were measured for each 6 in ×6 in sample andaveraged to obtain a mean sample weight that was used to calculate anormalized hydrostatic head. The results are shown in Table 6 and showabout a 3.5 mbar higher hydrostatic head for samples prepared usingflattened belts compared to comparative examples made using round beltsover the entire range of line speed. TABLE 6 Hydrostatic Headmeasurements for Examples 17-21 and Comparative Examples F-J Comp CompComp Comp Comp Ex. F Ex. G Ex. H Ex. I Ex. J Ex. 17 Ex. 18 Ex. 19 Ex. 20Ex. 21 Belts Belt B Belt B Belt B Belt B Belt B Belt BF Belt BF Belt BFBelt BF Belt BF Belt A Belt A Belt A Belt A Belt A Belt A1F Belt A1FBelt A1F Belt A1F Belt A1F Line Speed 35 40 45 50 55 35 40 45 50 55(yd/min) I × E 5.29 × 4.63 × 4.12 × 3.71 × 3.36 × 5.29 × 4.63 × 4.12 ×3.71 × 3.36 × (hp-hr-lb_(f)/lb_(m)) 10⁻³ 10⁻³ 10⁻³ 10⁻³ 10⁻³ 10⁻³ 10⁻³10⁻³ 10⁻³ 10⁻³ Mean  1.610  1.626  1.622  1.667  1.671  1.659  1.653 1.673  1.672  1.677 Sample wt (g) Mean HH 23.1 24.6 24.0 23.5 23.8 27.428.3 27.5 26.9 26.3 (mbar) Normalized 23.7 25.0 24.5 23.3 23.5 27.3 28.327.2 26.6 25.9 HH² % Increase 15% 13% 11% 14% 10% in HH²Hydrostatic head normalized to a sample weight of 1.653 g

In the table above and elsewhere in the specification, I×E is the energyimpact product delivered by water jets impinging on the fabric web andis calculated as described in U.S. Pat. No. 5,459,912 to Oathout, whichis incorporated by reference herein.

Example 22-26 and Comparative Examples K-O

The samples in these examples were prepared as described for Examples17-21, except that I×E was varied by changing the jet profile instead ofthe line speed, which was held constant in these examples at 50 yd/min.The jet profiles were calculated to give the same I×E factors asExamples 17-21 and Comparative Examples F-J. The specific jet pressuresand belts used, as well as hydrostatic head values are reported in Table7. Similar to Examples 17-21 and Comparative Examples F-J, the frabricsof the present invention had about a 3 mbar improvement in hydrostatichead. TABLE 7 Hydrostatic Head measurements for Examples 22-26 andComparative Examples K-O Comp Comp Comp Comp Comp Ex. K Ex. 22 Ex. L Ex.23 Ex. M Ex. 24 Ex. N Ex. 25 Ex. O Ex. 26 Belts Belt B Belt BF Belt BBelt BF Belt B Belt BF Belt B Belt BF Belt B Belt BF Belt A Belt A1FBelt A Belt Belt A Belt Belt A Belt Belt A Belt A1F A1F A1F A1F I × E5.29 × 5.29 × 4.63 × 4.63 × 4.12 × 4.12 × 3.71 × 3.71 × 3.36 × 3.36 ×(hp-hr-lb_(f)/lb_(m)) 10⁻³ 10⁻³ 10⁻³ 10⁻³ 10⁻³ 10⁻³ 10⁻³ 10⁻³ 10⁻³ 10⁻³Jet P (psi) for Consolidation Jets CJ1, CJ2 and Entangling Jets 1-9 CJ1,CJ2 293,424 293,424 278,402 278,402 265,384 265,384 254,368 254,368109,163 109,163 1 131 131 124 124 119 119 114 114 109 109 2 196 196 185185 177 177 170 170 163 163 3 326 326 309 309 295 295 283 283 272 272 4522 522 495 495 472 472 453 453 435 435 5 1044 1044 990 990 945 945 906906 872 872 6 1085 1085 1028 1028 981 981 941 941 905 905 7 1085 10851028 1028 981 981 941 941 905 905 8 1175 1175 1114 1114 1063 1063 10191019 980 980 9 1175 1175 1114 1114 1063 1063 1019 1019 980 980 MeanSample 1.660 1.640 1.651 1.646 1.653 1.648 1.649 1.662 1.699 1.642 Wt(g) Mean HH 22.8 25.5 23.3 25.8 24.3 26.7 23.8 26.5 23.8 24.7 (mbar)Normalized 22.7 25.7 23.3 25.9 24.3 26.8 23.9 26.4 23.2 24.9 HH² %Increase 13% 11% 10% 10% 7% in HH²Hydrostatic head normalized to a sample weight of 1.655 g

Examples 27 and Comparative Example P

This example demonstrates use of a flattened metal screen to makenonwoven fabrics of the present invention. The paper and PET staplefiber layers were the same as those used in Example 1 and wereconsolidated and hydroentangled as described in Example 1 except thatflattened metal screen CF was used for Example 27 and round metal screenC was used for Comparative Example P (for both the consolidation andentanglement steps). The fabrics were treated with a repellent finish asdescribed in Examples 14-16. Examination of photomicrographs of the top(WP) and bottom (PET) layers showed that there was more WP on the PETside for Example 28 compared to Comparative Example P, however thedifference was not as significant as observed for similar samples thatwere entangled on plastic belts. The results are summarized in Table 8.Hydrostatic head values were measured for four samples for each exampleand averaged to obtain the HH value shown in the table. All propertieswere somewhat improved for the fabric of the invention compared to thecomparative example. TABLE 8 Strength, Abrasion, and HH Properties forExample 27 and Comparative Example P Comparative Example P Example 27Strength, MD (lb_(f)) 25.91 26.34 Strength, CD (lb_(f)) 24.16 24.92 Avg.BW, MD, CD¹ (oz/yd²) 1.6,1.7 1.7,1.7 MD Strength/CD Strength  0.93  0.95Avg Strength [(MD + CD)/2] (lb_(f)) 25.04 25.63 % Increase in AvgStrength   2% Martindale Abrasion 1.3 1.2 Hydrostatic Head (mbar) 22.8 23.8  % Increase in HH 4.4%¹average basis weight was calculated and reported for samples used tomeasure MD strength and samples used to measure CD strength

1. A nonwoven fabric, comprising wood pulp and synthetic fibers, made bya hydroentangling process using at least one woven support membercomprising substantially round strands having knuckle areas at theintersection of warp and weft, wherein the knuckle areas are conditionedto achieve a flattened land area, wherein the fabric has an increase ineach of tensile strength, hydrohead and abrasion resistance compared toa substantially equal fabric made by a hydroentangling process using asupport member wherein the knuckle areas have not been conditioned toachieve a substantially flattened land area.
 2. A nonwoven fabric havinga top surface and a bottom surface, comprising wood pulp and syntheticfibers and the fabric is made by a hydroentangling process using atleast one woven support member comprising substantially round strandshaving knuckle areas at the intersection of warp and weft, wherein theknuckle areas are conditioned to achieve a flattened land area, andwherein the bottom surface has a larger percentage of wood pulp relativeto the top surface of the fabric compared to a substantially equalfabric made by a hydroentangling process using a support member whereinthe knuckle areas have not been conditioned to achieve a substantiallyflattened land area.
 3. The nonwoven fabric of claim 1 or 2, wherein thestrands are selected from the group consisting of metal and plastic. 4.The nonwoven fabric of claim 3, wherein the knuckle areas of the metalstrands are flattened by grinding.
 5. The nonwoven fabric of claim 3,wherein the knuckle areas of the plastic strands are flattened bycalendering.
 6. The nonwoven fabric of claim 4, wherein the percentageof diameter removed of the strands is at least about 20%.
 7. Thenonwoven fabric of claim 5, wherein the maximum aspect ratio of thestrands is about 0.75.
 8. The nonwoven fabric of claim 1 or 2, whereinthe synthetic fiber is selected from the group consisting of polyester,polyolefin and polyamide.
 9. The nonwoven fabric of claim 1 or 2,wherein the nonwoven fabric is made by pre-consolidating a syntheticfiber web on a round belt followed by positioning a wood pulp layer onthe top of the synthetic fiber web and hydroentangling the wood pulplayer and the web on a flattened belt.
 10. The nonwoven of claim 1 or 2,wherein the nonwoven fabric is made by pre-consolidating a syntheticfiber web on a first flattened belt followed by positioning a wood pulplayer on the top of the synthetic fiber web and hydroentangling the woodpulp layer and the web on a second flattened belt.